1. Field of the Invention
The present invention relates to an image forming apparatus such as a facsimile, a printer and the like, and more particularly, it relates to an image forming apparatus in which an automatic sheet separating and conveying mechanism is improved.
2. Related Background Art
In many original reading portions of conventional image forming apparatuses (for example, an original reading portion of a facsimile), an automatic original separating and conveying mechanism for automatically separating originals one by one and for conveying the separated original is provided for permitting the setting of a plurality of originals for transmission. In many original separating and conveying mechanisms, a separation piece is contacted with a separation roller by urging the separation piece against the separation roller by means of an elastic member such as a spring.
In such a separating and conveying mechanism, the separation roller is rotated in an original conveying direction to separate a single sheet (paper sheet) contacted with the separation roller from the other paper sheets, by utilizing differences in a friction force between the paper sheets, a friction force between the paper sheet and the separation piece and a friction force between the paper sheet and the separation roller.
In the facsimile apparatus, various sheets such as thick paper sheets, thin paper sheets or sheets having weak stiffness may be used as originals. The friction force between the sheets, friction force between the separation roller and the sheet, and friction force between the separation piece and the sheet are greatly varied with temperature, humidity and/or sheet material.
Thus, in order to ensure that the originals can positively be separated even if such conditions are changed, there have been proposed a mechanism for adjusting the friction forces by changing a length of the elastic member for urging the separation piece in accordance with the kind of the sheet, and a mechanism for releasing the separation piece from the separation roller (for example, disclosed in Japanese Patent Application Laid-Open No. 59-13256).
In case of a multi-function facsimile having a color copying function or a function as a scanner connected to a computer and adapted to send a color image to the computer, as well as transmission and reception functions, a sheet different from a sheet used for transmission is used as an original.
For example, such an original may be a scrap of a newspaper, a color photograph, a color page of a magazine or a visiting card. The scraps of the newspaper and the magazine are formed from a thin paper sheet normally having both surfaces on which images are printed. When such a scrap (original) is conveyed, it is important that the original is not damaged and the rear surface of the original is not contaminated as well as the front surface.
In the conventional facsimile apparatuses, regarding the conveyance of the sheet, a function for positively separating an original bundle has been emphasized. To this end, the separation piece has been formed from rubber material having great coefficient of friction. As is in the conventional cases, even when the urging force is weakened, since the coefficient of friction of the separation piece is great, there is a danger of damaging or scratching the original. Due to rubbing between the original and the rubber material used in the separation piece, a rubber mark (rubber powder) of the separation piece is adhered to the rear surface of the original. On the other hand, when a thick and hard sheet such as a visiting card is used as the original, it is difficult to convey the sheet only when the urging force is weakened.
In consideration of the above, in order to ensure that the thick sheet (such as a visiting card) is positively conveyed, a photograph and a newspaper are conveyed without damage and without adhering the rubber mark onto the rear surface, a mechanism for completely separating the separation piece from the separation roller is required.
In the conventional techniques, a purpose for releasing the separation piece was that the original which was damaged during the conveyance is removed. Thus, in an arrangement, at the same time when the separation piece is released, an auxiliary convey portion is also separated. Accordingly, when such an arrangement is applied to the original conveyance, a tip end of the original must be inserted up to a reading position (located at a deeper portion of the apparatus).
The visiting card has a feature that not only it is thick but also it has a small size. It is difficult to set the visiting card without any bending during the insertion of the card. Further, when the visiting card is inserted, since the conveyance of the card from a sheet insertion opening is effected only by the separation roller, it is difficult to achieve stable conveyance (a tip end of the card is apt to be skew fed).